Electromagnetic relays



Oct. 29, 1957 F. E. ROMMEL ET AL 2,811,602

ELECTROMAGNETIC RELAYS 2 Sheets-Sheet 1 Filed May 15, 1953 ,v 57 F. E. ROMMEL El AL 2,811,502

L ELECTROMAGNETIC RELAYS Filed May 15, 1953 2 Sheets-Sheet 2 Inventor: Freder/ak E, Fomme/ Fupr? EH, Carpenfer United States Patent 2,81 1,602 Patented Oct. 29, 1957 Free ELECTRQMAGNETTC RELAYS Frederick Emil Rommel, Ilford, and Rupert Evan Howard Carpenter, South Croydon, England; said Rommel assignor to Telephone Manufacturing Company Limited, London, England, a British company Application May 15, 1953,- Serial No. 355,322 Claims priority, application Great Britain May 29, 1952 6 Claims. (Cl. 208-93) This invention relates to polarised electromagnetic relays and, more particularly, to one-side-stable relays.

Most forms of polarised relays provided with an armature of magnetic material depend for their operation on a balance between the torque exerted mechanically on the armature by a spring and the torque exerted magnetically on the armature and produced by the polarising magnet system. The mechanical torque imparts positive stiifness to the armature and tends to hold the armature in a neutral position between the opposite side contacts while the 'magnetic torque produces a negative stiffness and tends to draw the armature out of a position of unstable equilibrium between the said contacts and towards the nearest pole piece.

In the case of a both-sides-stable relay, the magnetic stiffness is greater than the mechanical stiitness so that the resultant stiffness is negative and consequently, the armature moves from the position of unstable equilibrium with increasing force until it is arrested by one of the side contacts.

In order to produce the desired operation of a one-sidestable relay, it has been customary to set over one of the side contacts towards and beyond the central position and to set the opposite side contact to yield the desired contact gap. Then, of course, the armature is prevented from taking up the central position and consequently, the part of the armature within the working air gap of the relay only traverses a portion of that part of the air gap which is on one side of its central plane during an excursion of the armature from one side contact to the other. This means that for a given magnetic gap, the available ex cursion at the contacts is greatly curtailed.

In accordance with the present invention, the contacts or other stops which define the angular working range of the armature are arranged so that the two extreme angular positions of this range are reached by moving the armature in opposite directions from the central plane of the working air gap, and in addition the mechanical and magnetic torques are arranged to vary linearly over the said range at rates which, if continued outside the said range, would cause the said torques to become zero at substantially the same virtual positions of the armature. By this invention, the above drawback is eliminated and the armature can play across nearly the whole length of the working air gap. The armature is prevented from reaching the virtual position referred to by encountering one of the contacts at the end of its movement towards this virtual position.

There is no diliiculty in setting over the mechanical torque on the armature because this only requires the biassing of a spring, which is usually the armature suspension spring. The setting over of the magnetic torque, however, may be dealt with in a number of ways, in fact among others, by changing the strength of the permanent flux entering or leaving the armature on one side with respect to that entering or leaving it on the other side, or again by changing the point of action of the resultant magnetic force on the armature with respect to the pivot of the latter.

The invention can be more easily appreciated by considering the action of the customary arrangements and by following the description of certain examples of relays in accordance with the present invention with reference to the accompanying drawings, in which:

Figure l is a diagrammatic representation of the magnetic system and armature of the well-known Carpenter relay such as disclosed in U. S. Patents 1,826,990 and 2,412,123.

Figures 2 and 3 are force diagrams illustrating respectively the operation of a relay as shown in Figure 1 and the relays according to the present invention;

Figure 4 is a similar explanatory diagram showing difierent conditions;

Figures 5 and 6 are diagrams similar to Figure l but showing two forms of the present invention;

Figures 7 and 8 are elevations seen from opposite sides of a relay according to U. S. Patent 2,559,399 constructed in accordance with the present invention, the armature, the contacts and the magnet nearest to the observer, however, being omitted, and

Figures 9 and 10 are similar diagrams to Figures 5 and 6 illustrating the application of the invention to two other recognised forms of moving-iron polarised relays.

Referring first of all to Figures 1 and 2, Figure 1 will be recognised as a counterpart of Figure 5 of the drawings of Patent 2,412,123, except that the side contacts c, c have been set over to the right of the centre line A, B and it will be observed that even the left hand contact 0 is set over beyond that centre line. This means that when the signal winding w is not energised, the top end of the armature a tends to move to the right of the neutral position but is arrested by contact with the side contact c, thereby producing the one-side-stable action. The armature a is pivoted at p between permanent magnets m and m and it can easily be seen that owing to the setting of the side contacts c, c the travel of the armature is restricted and its lower end can only traverse a fraction of the gap between the magnetic limbs l and I.

In Figure 2, the planes of the faces of the limbs l, l are shown at x, y. The neutral or balanced position of the armature which is here central, is seen at the point 11. For the small excursions which here come into question, the mechanical force and the magnetic force are both to a first approximation linearly proportional to the distance of the armature from the central position at n, and as the relay is inherently side-stable, the magnetic force represented by the full line Ma, that is to say the force proportional to the negative stiffness, is greater than the mechanical force represented by broken line Me, which is proportional to the positive stiffness. The magnetic force is greater as shown by the greater slope of the line Ma. The chain line R is the resultant of the forces Ma, Me and also, of course, is directly proportional to the distance of the armature from the central position n. Thus, when the winding w is not energised, the resultant force R would cause the aramture a (in Figure 1) if not restrained by contact 0 to move over clockwise with increasing force.

Now considering the present invention, Figure 3 is a diagram similar to Figure 2 and the same reference charactors have been applied. It will be seen in this case that the point of balance or the virtual neutral point n at which both the mechanical torque Me and magnetic force Ma would be reduced to zero it continued at the same rate to the left of position 0, has been thrown over to the left. The result of this is that the resulting force F. when the relay is not energized, would throw the armature a away from that point and into the end position 0, consequently, the side contacts which are shown in the diagrams of Figures 2 and 3 at 0, 01, are more widely separated and centrally placed with respect to the central plane Cp of the relay. Therefore, the distance between the points of the contacts 0, c1 in Figure 3 represents the useful air gap which it can be seen may be set at any value up to the full gap between the faces x, y. A comparison with Figure 2 shows clearly the fact already mentioned, that by setting the contacts 0, 01 to the right to secure the one-side-stable eifect, the useful air gap is reduced to less than half of the actual air gap.

The point It in Figure 3 is the apparent or virtual zero point for both the mechanical and magnetic torques applied to the armature when varied at rates represented by the slopes of lines Ma and Mc between the points and c Actually, the magnetic torque does not vary in a straight line to the left of position c in Figure 3, but it is not important to take this into consideration since the armature never operates in this range.

The reason for making the magnetic torque Ma and the mechanical torque Me have apparent zero points at or near to the same point It, can easily be appreciated from the diagram in Figure 4 which is drawn with the lines Ma, Me crossing the horizontal axis at different points 0, 0. For example, it due to temperature change the mechanical stiffness is increased, the slope of the line Me will be increased as shown at Me and the slope of the resultant line R will be reduced as shown at R hence the point at which it crosses the horizontal armature displacement axis is shifted from n to n. This means that the neutral position of the armature will shift along the horizontal axis, which results in a serious alteration of the values of exciting current in the winding w at which the relay will operate for the armature to be drawn against the side contact cl and at which it will be released. This in turn causes a serious alteration in the bias of the relay. The shift of the neutral position can also result, as shown in Figure 4, in a dangerous reduction in the restoring torque away from the contact 0 when the energizing current is removed. The reduction is indicated as from f to f in that figure.

If 11' should be shifted beyond the position of the face of the contact c which is shown at p, this torque would change in sense and the one-side-stable action be lost altogether.

In Figure a form of relay is shown in which the present invention is applied to a magnetic system as set forth in U. S. Patents 1,826,990 and 2,412,123, that is to say, in general, the relay follows that shown in Figure l with two main differences. The first is that the side contacts 0, 01 are not set over but are set at equal distances on opposite sides of the central plane A, B of the air gap between the limbs l, l, and secondly, the system is unbalanced by placing the polarising permanent magnet m so that its face at the inner end is further from the armature a than is the corresponding inner face of the other magnet m1. In the example shown, this is effected by making the permanent magnet m shorter than the magnet ml. The result of this is, of course, that the flux at the magnetic limb l is greater than at the face of the limb I so that when the relay is not energised, the armature a tends to be moved by the resultant flux in the counterclockwise direction and is, therefore, one-side-stable against the side contact 0 as shown. The armature suspension spring s is set over so that the mechanical restoring torque which it exerts on the armature (and which is always less than the torque arising from the polarising magnetic fluxes) is greatest when the armature rests against the contact 0 and decreases as the armature moves from this position, becoming zero at the virtual point of polar faces of the permanent magnets in and m1 at different points with respect to the pivot P of the armature a. In this case, the armature control spring s is set over so that the balanced position is displaced counterclockwise and when the relay is not energised, the armature is turned clockwise by the dominating magnetic bias and is one-side-stable against the side contact 01.

In Figures 7 and 8 the invention is shown applied to a relay of the kind set forth in Patent 2,559,399 wherein the two permanent magnets m, ml overlap, and the armature vibrates at right angles to these magnets in the gap between them. Figures 7 and 8 are elevations seen from opposite sides of the relay and corresponding to Figure l of the drawings of Patent 2,559,399, except that in that figure the armature 13 and the front magnet 9 are omitted, and certain other details which are not shown are as in that prior Specification. Thus, it can be seen that the polar faces of the magnets m, m1 face the armature at different heights with respect to the pivot of the armature, and although the fluxes passing from the magnets m, m" into the armature are of the same order, in this case, they act at different lever arms and thence the magnetic outof-balance on the armature is established.

in Figure 9, the invention is shown applied to another known form of relay in which the armature a is pivoted at p near the upper ends of the magnets m, m. Thus, as in Figure 6 the permanent magnets m, m present their polar faces to the armature a at different heights with respect to the pivot P and the armature springs s are also set as in Figure 6 so that when no current is flowing in the windings w, the armature is set over clockwise by the dominating magnetic bias against the contact 0. The side contacts c, c1 are placed centrally at equal distances on opposite sides of the central plane A, B of the air gap between the magnetic limbs l, I. In view of what has been stated above, the armature control springs s are set over so that the mechanical torque on the armature a is zero in the same position of the armature as that at which the magnetic torque is zero.

Finally, in Figure 10 the invention is applied to the type of relay in which the armature a is pivoted centrally at P and is surrounded by the exciting winding w while the polarising flux is established by a horseshoe magnet m so that the flux from the pole N splits and passes upwardly and downwardly in the pole-piece t as shown by the arrows x, passes across the armature a at the top and bottom into the pole-piece t1 and reunites at the pole S. Again the side contacts 0, c1 are placed centrally at equal distances on opposite sides of the mid-plane A, B, of the air gaps. The magnetic torque is set over by displacing the upper tip r of the pole-piece t upwardly with respect to the tip r of the pole-piece t1 and by displacing the lower tip r2 of the pole-piece t upwardly with respect to the tip r3 of the pole-piece t1 so as to set over the armature counterclockwise. As before, the mechanical torque is set over to the same neutral point by biasing the armature control springs s which tend to rotate the armature in a clockwise direction.

We claim:

1. A one-side stable electromagnetic relay comprising a polarized magnetic structure formed with an air-gap at which the polarizing flux appears, an armature of magnetic material pivotally mounted to vibrate in said airgap, moving contact means actuated by said armature, a pair of stops in co-operative relationship with said moving contact means and defining for said armature an angular working range, the two extreme angular positions of said range being reached by moving said armature in opposite directions from the central plane of said air gap, at least one of said stops being an electrical contact, a signal winding linked with said magnetic structure, and means for applying a mechanical restoring torque to said armature, both said mechanical restoring torque and the magnetic torque produced by said polarizing flux acting on said material pivotally mounted to vibrate in said air-gaps,

moving contact means actuated by said armature, a pair of stops in co-operative relationship with said moving contact means and defining for said armature an angular working range, the two extreme angular positions of said range being reached by moving said armature in opposite directions from the central plane of said air gap, at least one of said stops being an electrical contact, a signal winding linked with said magnetic structure, and means for applying to said armature a mechanical restoring torque which varies in magnitude linearly with the position of the armature and at a rate which if continued beyond the range of travel of the armature would cause said mechanical torque to be reduced to zero at a virtual position of said armature lying outside the working range of travel of said armature, said magnetic structure having its polar faces at one of said air-gaps so arranged with respect to said armature that the strength of the polarizing fluxes passing between said polar faces respectively and the armature are unequal on the opposite faces thereof to effect a linear variation in the magnetic torque acting on said armature at a rate which if continued beyond the range of travel of the armature would cause said magnetic torque to be reduced to zero when said armature is in substantially the said virtual position.

3. A one-side stable electromagnetic relay comprising a polarized magnetic structure formed with air-gaps at which the polarizing flux appears, an armature of magnetic material pivotally mounted to vibrate in said airgaps, moving contact means actuated by said armature, a pair of stops in co-operative relationship with said armature and defining for said armature an angular working range, the two extreme angular positions of said range being reached by moving said armature in opposite directions from the central plane of said air gap, at least one of said stops being an electrical contact, a signal winding linked with said magnetic structure, and means for applying to said armature a mechanical restoring torque which varies in magnitude linearly with the position of the armature and at a rate which if continued beyond the range of travel of the armature would cause said mechanical torque to be reduced to zero at a virtual position of said armature lying outside the working range of travel of said armature, said magnetic structure having its polar faces at said air-gaps so disposed with respect to said armature that the polarizing magnetic flux acts on said armature on opposite sides thereof at points at different distances along said armature to provide a varying magnetic torque acting on said armature and having an apparent zero point at substantially said virtual position of the armature,

4. A one-side stable electromagnetic relay comprising a polarized magnetic structure formed with air-gaps at which the polarizing flux appears, an armature of magnetic material pivotally mounted to vibrate in said airgaps, at least one spring attached to said armature for imparting a mechanical restoring torque thereto, a pair of moving contacts mounted on opposite faces of said armature, a pair of substantially symmetrically located side contacts in co-operative relationship respectively with said moving contacts and fixing for said armature an angular working range, the two extreme angular positions of said range being reached by moving said armature in opposite directions from the central plane of said air gap, a signal winding linked with said magnetic structure, said mechanical restoring torque and the magnetic torque produced by said polarizing flux and acting on said armature being varied over the range of movement of said armature and at rates which it continued beyond the range of travel of the armature would be zero at substantially the same virtual angular position of said armature, said virtual angular position lying outside the working range of travel of said armature.

5. An electromagnetic relay according to claim 1, wherein the polar faces at one of said air-gaps are located at unequal distances from the respective adjacent surfaces of said armature.

6. An electromagnetic relay according to claim 3, wherein said magnetic structure is formed at one of said air-gaps with polar tips shaped to be unsymmetrical on opposite sides of said armature.

References Cited in the file of this patent UNITED STATES PATENTS 1,191,976 Kettering July 25, 1916 1,426,993 Kardaetz Aug. 22, 1922 1,541,618 Brown June 9, 1925 1,743,494 Snyder Jan. 14, 1930 1,826,990 Carpenter Oct. 13, 1931 2,351,588 Field June 20, 1944 2,412,123 Carpenter Dec. 3, 1946 2,515,771 Hall July 18, 1950 2,597,873 Kesselring May 27, 1952 2,619,560 Jepson et a1 Nov. 25, 1952 

